The embodiments described herein relate to estimating casing wear in the oil and gas industry.
Wellbores in the oil and gas industry are typically drilled in stages. Once a stage is drilled, it is often lined with a casing to provide wellbore wall stability to mitigate collapse and blowouts as additional stages are drilled. Because of this staged drilling and casing method, subsequent stages further from the surface typically exhibit a decrease in wellbore diameter.
When drilling below cased portions of the wellbore, the casing may wear due to contact with the drill string. Drilling involves not only drilling into new portions of the formation, but also reciprocation operations where the drill bit is moved up and down newly drilled portions of the wellbore (sometimes referred to as “stages”) to smooth the wellbore surface and provide a uniform wellbore diameter. As the drill string is reciprocated, the drill string proximal to the casing uphole of the drill bit cause wear on the casing.
Casing wear results in a decrease in casing thickness, which, in turn, weakens the casing. In order to avoid casing collapse or blowouts, it is advantageous to know the degree of wear that has taken place so that remedial actions may be taken when the casing thickness has sufficiently reduced. For these reasons, it is valuable to be able to determine the thickness of the casing at any given point.
The casing thickness may be determined spectroscopically by, for example, gamma rays tools. Such tools may be used after drilling the wellbore via a wireline operation to assess the casing thickness. However, this provides only a final assessment of the casing and does not allow for analysis of the casing thickness or integrity during the drilling operation itself.
To investigate casing thickness during drilling, such analysis tools may be placed along the drill string. However, the analysis tool can only assess the casing within a few feet along the wellbore relative to the analysis tool's current location. Accordingly, this does not provide an accurate assessment of the casing along the entire length of the wellbore.